1. Technical Field
The present application relates to door closer, and in particular a concealed door closer.
2. Background Art
At present, door closers and especially some concealed door closers are more and more widely used. These concealed door closers may be hidden in doors or door frames and drive the doors to rotate via a concealed slide rail and a rock arm, thereby maintaining intrinsic aesthetic qualities of the doors. The existing door closers are usually mounted externally and employ gear mesh transmission to realize a 90-degree transmission connection between the input shaft and the output shaft. However, such a structure has many disadvantages. Firstly, such a structure has a large size. In order to conveniently mount a concealed door closer in a door or door frame and to maintain aesthetic qualities of the door, it is preferable to use a door closer of a small size, so the size of the door closer is very important. Secondly, such a structure achieves a low transmission efficiency. An externally mounted door closer needs a large rotation force, and a low transmission efficiency of the bevel, gear leads to a large drive load for the motor in the door closer, thereby greatly reducing the life span of the motor. Thirdly, such a structure requires high precision in the mounting position. Due to the manner of gear mesh connection, the output shaft and the input shaft must form an angle of 90 degrees; otherwise the gear mesh connection will be affected.
When a door closer and especially an electric door closer is used, the motor of the door closer drives the input shaft to rotate, and the input shaft then drives the output shaft to rotate. Sometimes, the door may not be opened or closed in a normal automatic mode, or some malicious or accidental man-made damage may occur, causing the output shaft to be suddenly jammed. In this case, the transmission mechanism and the drive motor of the door closer may be severely damaged. After multiple damages, the operation of the door closer may be easily affected, and the door closer may be even broken.
Moreover, an instrument for measuring the rotation angle of the output shaft is often mounted on the door closer. In the prior art, a contact portion is arranged between the output shaft and the instrument for measuring the rotation angle of the output shaft. After the measurement is done many times, the contact portion may have a positional shift, and measurement errors may be increased, thereby shifting the door closer at the door closing position and even making it impossible to close the door.